1. Field of the Invention
The present invention relates generally to gyro compass for ships or the like and more particularly to a fast settle apparatus thereof.
2. Description of the Prior Art
An example of a gyro compass to which a fast settle apparatus of the present invention is applied will be described with reference to FIG. 1. FIG. 1 shows such a gyro compass that is disclosed in Japanese Pat. No. 428317.
In FIG. 1, reference letter A generally shows a gyro compass which includes a gyro case 1. The gyro case 1 incorporates therein a gyro rotor which is rotated by an induction motor at high speed and at a constant rotational speed though not shown. The rotation vector of the gyro rotor is oriented to the south (in the clockwise direction as viewed from the north side N). The gyro case 1 has a pair of vertical shafts 2, 2' projected therefrom at its top and bottom. These vertical shafts 2, 2' are respectively engaged with inner rings of ball bearings 4, 4' secured to corresponding positions of a vertical ring 3 which is provided outside the gyro case 1. The lower end of a suspension wire 5 is fixed to the upper vertical shaft 2 and the upper end of the suspension wire 5 is secure to the vertical ring 3 via a suspension wire attaching base 5'.
With the above-mentioned structure, the weight of the gyro case 1 does not become any thrust load for the ball bearings 4, 4' of the vertical shafts 2, 2' but it is thoroughly received by the suspension wire 5. Thus, the friction torque of the ball bearings 4, 4' can be reduced considerably. A pair of liquid ballistics 6 are attached to the vertical ring 3 at its east and west to give the gyro a north-seeking torque.
The pair of liquid ballistics 6 will be described more in detail with reference to FIG. 2. As shown in FIG. 2, each of the liquid ballistics 6 is a kind of communicated tube shape which comprises liquid reservoirs 6-1', 6-1 located on the south and north of gyro, liquid 6-2 of high specific gravity filling almost half of the liquid reservoirs 6-1', 6-1, an air tube 6-3 which communicates the south and north liquid reservoirs 6-1, 6-1' in the upper sides and a liquid tube 6-4 which communicates the same in the lower sides.
Referring back to FIG. 1, the gyro case 1 has a damping weight 7 secured to its west side portion to damp or suppress the north-seeking movement of the gyro. Also, the gyro case 1 has mounted on its east side portion a primary coil 8-1 of a differential transformer to detect a relative displacement angle between the gyro case 1 and the vertical ring 3 about the vertical shafts 2, 2'. The vertical ring 3 has a secondary coil 8-2 of the differential transformer mounted thereon at its positive opposing to the primary coil 8-1. The primary and secondary coils 8-1 and 8-2 constitute a follow-up pickup 8. Further, the vertical ring 3 has a pair of horizontal shafts 9, 9' projected therefrom outwardly at its east and west side positions perpendicular to both the vertical shafts 2, 2' and the gyro spin axis. These horizontal shafts 9, 9' are respectively engaged with inner rings of ball bearings 11, 11' secured to the corresponding positions of a horizontal ring 10 located outside the vertical ring 3. Also, the horizontal ring 10 has a pair of gimbal shafts 12, 12' mounted thereon at its position perpendicular to the horizontal shafts 9, 9' within the horizontal plane. These gimbal shafts 12, 12' are respectively engaged with a pair of gimbal shaft ball bearings 14, 14' secured to a follow-up ring 13 located outside the horizontal ring 10.
The follow-up ring 13 has follow-up shafts 15, 15' mounted thereon at its upper and lower portions as shown in FIG. 1. These follow-up shafts 15, 15' are engaged with follow-up ring bearings 17, 17' which are secured to a binnacle 16 at its corresponding positions, respectively.
The upper follow-up shaft 15 has a compass card 18 mounted thereon at its upper end. The binnacle 16 has a lubber line 18B fixed thereto at its position corresponding the ship's heading. Accordingly, a ship's azimuth angle is read out in the collaboration o the compass card 18 and the lubber line 18B. The binnacle 16 has an azimuth servo motor 19 mounted on the lower portion thereof. The azimuth servo motor 19 has a rotating shaft 19A which is coupled through an azimuth pinion 20 to an azimuth gear 21 located under the follow-up ring 13. The binnacle 16 has an azimuth transmitter 22 mounted on the lower portion thereof, and a rotating shaft 22A of the azimuth transmitter 22 is meshed with the azimuth gear 21 via a gear system (not shown) to transmit an azimuth signal in the form of an electrical signal to the outside.
The parts within the horizontal ring 10, i.e., parts including the horizontal ring 10, the vertical ring 3, the gyro case 1 and so on constitute a so-called sensitive element. The sensitive element forms a physical pendulum, whose lower portion is heavier than its upper portion, around the gimbal shafts 12, 12' thereby to keep the horizontal shafts 9, 9' within the horizontal plane at all times regardless of the inclination of ship's body or hull.
When there is a difference between the azimuth of the gyro case 1 and the azimuth of the vertical ring 3, the follow-up pickup 8 provided therebetween detects the difference and converts the detected difference into an electrical signal. This electrical signal is amplified by a servo amplifier 23 located outside the gyro compass 1 and applied to the azimuth servo motor 19 (azimuth servo system). The rotation of the azimuth servo motor 19 caused thereby is transmitted through its rotating shaft 19A, the gear series and the azimuth gear 21 to the follow-up ring 13 and is further transmitted through the horizontal ring 10 and the horizontal shafts 9, 9' and so on to the vertical ring 3, thus keeping the vertical ring 3 and the gyro case 1 have no azimuth displacement therebetween at all times.
Owing to the action of the azimuth servo system, the horizontal shafts 9, 9' and the gyro spin axis are always made in a perpendicular relationship and no twisting torque of the suspension wire 5 is applied to the gyro at all Specifically, owing to the actions of the three axes, 9' and the gimbal shafts 12, 12' of the servo system, the gyro case 1 is perfectly isolated from the angular motion of ship's hull, thus a gyroscope being constructed.
The above-mentioned liquid ballistic 6 gives the gyroscope the north-seeking torque, i.e., a function as a compass.
The principle of the liquid ballistic 6 will be described next with reference to FIG. 2. FIG. 2 illustrates a case where the north-seeking end of the gyro is lifted up relative to the horizontal plane HL by an angle .theta..
In this embodiment, let it be assumed that the ship is brought to stop. THen, the surface L1 of the liquid 6-2 is perpendicular to the direction of acceleration of gravity g. Accordingly, as compared with a case where there is no inclination in the gyro, the liquid shown by the hatched area in FIG. 2 is decreased in the liquid reservoir 6-1' on the north side while increased in the liquid reservoir 6-1 on the south side. Now, r1 assumes the distance from each of the horizontal shafts 9, 9' to the center of each of the liquid reservoirs 6-1, 6-1'; S assumes the sectional area of each of the liquid reservoirs 6-1, 6-1' and .theta. assumes the specific gravity of the liquid 6-2. Then, the weight of the liquid in the inclined portion is expressed as EQU S.times.r1 sin .theta..times..rho..times.g
The above umbalance of weight occurs in both the liquid reservoirs 6-1, 6-1' on the south and north sides and the moment arm from each of the horizontal shafts 9, 9' is r1 so that a torque T.sub.H that is generated by the liquid ballistic 6 around the horizontal shafts 9, 9' when the north-seeking end of the gyro is inclined by the angle .theta. is approximately expressed as EQU T.sub.H =2S r1.sup.2 g.rho..theta.
In this case, EQU 2S r1.sup.2 g.rho.=K
is assumed where K is called the ballistic constant. In other words, the liquid ballistic 6 applies the torque proportional to the inclination of the gyro spin axis relative to the horizontal plane to the gyro around its horizontal shafts 9, 9' so that the gyro is given the north-seeking torque, thus being made as a gyro compass.
On the other hand, the damping weight 7 is mounted on the gyro case 1 with a distance r2 (in the direction perpendicular to the sheet of drawing) from the vertical shafts 2, 2' within a plane including the vertical shafts 2, 2' and which is also perpendicular to the gyro spin axis as shown in FIG. 3. FIG. 3 illustrates, as viewing on the west side, the gyro case 1 which is placed in such a condition that the north-seeking end of gyro is inclined upward (or lifted up) relative to the horizontal plane HL by the angle .theta.. As FIG. 3 shows, since gravitational acceleration g acts on the damping weight 7 with mass m, the force of m.times.g is applied to the damping weight 7 in the vertical direction. Then, let it be considered that this force n.times.g is analyzed into a component m g cos .theta. parallel to the horizontal shafts 2, 2' and a component m g sin .theta. parallel to the spin axis. Of these components m g cos .theta. and m g sin .theta., the component m g cos .theta. parallel to the vertical shafts 2, 2' acts only as the load for the ball bearings 4, 4' of the vertical shafts 2, 2'. Whereas, the component m g sin .theta. parallel to the spin axis is multiplied with the distance r2 from the vertical shafts 2, 2' and acts on the gyro as the torque around the vertical shafts 2, 2'. T.phi. assumes this torque. Then, the torque T.phi. is approximately expressed by the following equation EQU T.phi.=.mu..multidot..theta.
where .mu. is equal to m g r2.
In other words, the damping weight 7 is adapted to apply the torque proportional to the inclination of the gyro spin axis relative to the horizontal plane to the gyro around its vertical shafts 2, 2'. The north-seeking movement of the compass can be damped by the damping weight 7.
FIG. 4 is a block diagram used to explain the principle of the north-seeking operation of the above-mentioned gyro compass shown in FIG. 1. Particularly in the block diagram of FIG. 4, azimuth error .phi. and inclination angle .theta. of the north-seeking end of the gyro spin axis from the true north are taken as variable and the north-seeking movement (or the precession) of the gyro relative to initial errors .phi..sub.0, .theta..sub.0 thereof is expressed by Laplace operator and transfer function. In FIG. 4, g represents the gravitational acceleration, R the radius of the earth, .OMEGA. the angular velocity of earth's rotation, H the angular momentum of the gyro, .lambda. the latitude at that point, K the north-seeking constant (ballistic constant), .mu. the damping constant and S the Laplace operator, respectively.
If now there exists the azimuth error .phi., this azimuth error .phi. is multiplied with a horizontal component .OMEGA. cos .lambda. (100) of the angular velocity .OMEGA. of earth's rotation to produce an angular velocity input. This angular velocity input acts on an element 101 around the horizontal axis of the gyro thereby to produce together with the initial inclination angle .theta..sub.0 the inclination angle .theta. of gyro. By the inclination angle .theta. of the spin axis, the vertical ring 3 is inclined similarly and the liquid ballistic 6 mounted on the vertical ring 3 is also inclined so that the liquid 6-2 is moved to the inclined side liquid reservoir 6-1, thus producing a torque K.theta. around the horizontal axis of the gyro. This torque K.theta. is divided by the gyro angular momentum H and is then added with the vertical component .OMEGA. sin .lambda. of earth rotation angular velocity to produce an angular velocity input. This angular velocity input acts on an element 102 provided around the vertical axis of the gyro. This angular velocity input is added with the initial azimuth error .phi..sub.0 to produce the azimuth error .phi., by which the loop is closed. The loop is the north-seeking loop of the gyro compass. the solution of this loop becomes the oscillating solution because the loop contains two poles represented by 1/S. The torque .mu..theta., which results from multiplying the gyro inclination angle .theta. with the damping constant .mu., is divided by the angular momentum H to provide an angular velocity input. This angular velocity input is negatively fed back to the horizontal axis element 101 of the gyro so as to reduce the above-mentioned inclination angle .theta. so that the north-seeking movement of the north-seeking loop is damped. This latter loop is the damping loop.
The marine gyro compass is generally designed to make its north-seeking movement period about 90 minutes (condition of Schuler tuning) in order to avoid acceleration error from being produced in the gyro compass due to acceleration in the horizontal direction caused by increase and/or decrease of ship's speed, ship's turning and so one. As a result, it takes a lot of time (this time is referred to as a settling time) until the gyro compass becomes settled to the true north after having been actuated.
In most cases, the above-mentioned settling time is negligible for the standard ships in navigation. This long settling time becomes a problem that should be solved by the ship for special service.